1. Field of the Invention
The invention relates to the field of oil recovery and, more specifically, to the recovery of oil using elastic vibration energy and with rather high efficiency can be applied for recovering of oil from depths of over 2000 meters.
2. Description of the Related Art
The device for pulse impact on oil formation (pool) with a downhole apparatus is known with working idea based on ‘electro-hydraulic effect’ allowing to increase productivity of oil pool treatment.
In this device downhole apparatus is designed as empty cylindrical body and contains a charger, a unit of energy storage capacitors, a discharge unit with two electrodes and a trigger.
The major disadvantages of this device are: big size of a downhole apparatus (roughly diameter is 250 mm, length—3500 mm) and low energy (not more than 100-300 J) of single discharge of energy storage capacities.
The use of a downhole apparatus with such energy of discharge does not allow to work with depths of over 1500-2000 meters, while vast majority of wells e.g. in Western Siberia of Russian Federation and in Canada have oil formations (pools) on depths of 2500-2700 meters and more and its size makes difficult to work in pipe casing with reduced diameter with varying configuration of sections of pool and limits its move to other wells.
The second (and most important) disadvantage of this device is caused by ‘negative constructive features’ of a unit of energy storage capacitors.
Normally for increase of discharge energy, capacity energy is increased as discharge energy is equal to half of multiplication of capacity and squared voltage applied. However this leads to considerable size increase of downhole apparatus and makes more difficult use of it.
‘Negative constructive features’ of the unit of energy storage capacitors of the known device are that capacities both when charging and discharging have parallel electrical connection. Accordingly this approach does not allow to have discharging voltage more than 20 kW (limited by cable working capacity and safety requirements) and does not allow to obtain energy of discharge more than 1 kJ, which is however required (see Paschen curve in the analogue in FIG. 1) for efficient work on considerable depths.
There is no direct note for such (parallel) connection of charging capacities in the description of known invention but available information (see L.la.Popilov ‘Electro-physical and electro-chemical treatment of materials’ chapter 13 ‘Electro-hydraulic treatment’ pp. 265-270, FIGS. 1, 2 and 3) let us claim that authors of this invention used exactly this well-known and commonly used method for electrical connection of charging capacitors.
Besides, use in this device of electro-hydraulic effect causing elastic vibrations of only low frequency in fluent fraction of oil pool providing treatment of reservoir zone but does not allow to treat with vibration well bottom zone (as high frequency vibration is required), which could increase productivity of treated oil pool. Given disadvantage should be also associated with the method for oil recovery with use of this devise.
It is also known the method of oil recovery using energy of high frequency vibration generated by source of acoustic vibrations [2].
The use of elastic vibrations of high frequency does not prevent from placing of downhole apparatus on depth of 2700 meters but does not allow impacting on critical area of the well (as low frequency vibration is required), that could increase to greater extent productivity of treated oil pool.
This is the major disadvantage of described method of oil recovery and accordingly of the device used for it.
Apart from this, it is know the method for oil discovery using energy of elastic vibration of two frequencies in the range of 10-60 kHz including placing in a well on the working depth of downhole apparatus, initiation of elastic vibrations of various frequencies followed by mainly multiple impact with elastic vibrations of various frequencies on oil pool. This method is realized with use of the device in which downhole apparatus is connected to aboveground power supply and contains one ultrasonic emitting piezoelectric transmitter having rather narrow gain-frequency characteristic and providing generation of elastic vibrations of high frequency on its resonance frequency.
However this assembly (device) and, accordingly, based on its use the method for oil recovery with impact of elastic vibration on oil pool, which in its technical essence is closet to the invention and is used as the prototype, have a range of major disadvantages.
First, non-linearity of porous environment containing fluid may be not sufficient for conversion of pulse emission of piezoelectric transmitter pulsation of low frequency. Besides, as maximum amplitude of high-frequency vibrations remains the same and in case of pulsation is 103 times less than high frequency, intensity of emission of low-frequency will be 106 times less than the one of high frequency, which is obviously not enough for having any impact on pool. So, the use of one piezoelectric transmitter in different options of its stimulation does not allow to obtain elastic vibration of low frequency. Therefore, the known method and the known device with use of piezoelectric transmitter (authors of the known invention mention only piezoelectric transmitter) do not provide treatment of required area of a well.
Second, proposed by the authors of known invention impact by elastic vibrations of low frequency in the range of 10-15 kHz and impact by elastic vibration of high frequency in the range above 44 kHz are not optimal for treatment of oil pool.
Third, the known device does not provide and the known method does not take into consideration simultaneous impact with elastic vibration of high and low frequency, which in some cases may be very helpful.
Due to disadvantages listed above, the known method and device can be described as ones having low technical capabilities, which dramatically reduce efficiency of treatment of oil pool and do not allow increasing its productivity to required level.